Police have been asked to investigate an Essex hospital’s cancer services, after the health watchdog uncovered evidence that staff were pressured to change patient records to meet national targets.

The Care Quality Commission (CQC) has recommended that the Colchester Hospital University NHS Foundation Trust be placed in special measures, after unannounced inspections in August and September.

Inspectors found inaccuracies in data on cancer treatment waiting times, which they said may have led to some patients not getting the care they needed in time.

The trust has now written to 30 patients, or the next of kin in cases where patients have died, to offer face-to-face interviews to review their treatment, after the CQC raised concerns that their care may have been affected.

Discrepancies were found between data provided for national cancer waiting times records, and actual patient records. Of 61 care records examined, 22 suggested patients may have been put at risk of receiving unsafe or ineffective care because of delays in being assigned appointments.

Three members of staff reported being “pressured, bullied or harassed” to change official data on patients’ care pathways so as not to breach national guidelines. Inspectors said they had seen emails, minutes and letters showing that senior figures at the trust were aware of concerns raised by staff.

In some cases people did not get cancer treatment within the required 62 days and in three cases delays exceeded 100 days, the CQC said.

Sir Mike Richards, the chief inspector of hospitals, said that it was “shocking” that “people’s lives may have been put at risk for the sake of the waiting times figures”.

“If you are diagnosed with cancer you are entitled to think that your hospital will do all they can to ensure you get treatment you need as soon as possible... Clearly this report raises questions over the safety and effectiveness of these services. But it also raises questions at the highest level,” he said.

The foundation trust regulator Monitor has opened a formal investigation into the trust and said it would consider placing the trust into special measures. It would be the thirteenth NHS trust to face the sanction, which has resulted in hospital chief executives being removed from their post and health service “superheads” brought in to reform services.

Essex police said they had been contacted by the CQC and were reviewing the information provided to establish whether a criminal investigation is necessary.

Dr Sean MacDonnell, the trust’s medical director, apologised to patients but urged all cancer service users to “keep their appointments”.

“Both myself and staff throughout the trust are shocked and dismayed by the concerns raised in the CQC report,” he said. “Patients and the public can be reassured that we are taking the findings extremely seriously and are determined to get to the bottom of the issues and sort them out.”

He said suggestions that “inappropriate changes” had been made to records was “extremely disheartening”.

“It is essential that patients and staff can trust all of our employees to do the right thing. It seems that this has not always been the case,” he added. “If there is any evidence that any of our staff have inappropriately adjusted and reported cancer figures, the trust will take the strongest possible action against them.”

The trust was one of 14 investigated by NHS England’s medical director Sir Bruce Keogh in a review of hospitals with high mortality rates, but was not one of the 11 placed into special measures following his report, which was published in July.

The CQC also highlighted poor leadership at the trust and said an internal investigation into staff concerns in 2012 “failed to investigate the allegations thoroughly or follow up with the patients who were affected.”